It is well-known that, in an internal-combustion engine, the coolant, apart from its heat exchange function, also allows the engine cooling circuit to be protected from the main degradation forms which it is subjected to. Pitting corrosion, metal tearing by cavitation, electrochemical corrosion, . . . , are the most frequent degradation forms, which are likely to cause great disturbances or even engine damage if they are not detected in time.
In order to fulfill this protective function, coolants thus require a specifically designed formulation. They contain additives for protecting the various metals of the cooling circuit.
However, during operation, the formulation of the coolant may vary by decay or impoverishment of certain additives
This modification poses problems because the coolant may thus damage certain materials of the circuit.
It is currently necessary to change periodically and arbitrarily the coolant in order to avoid circuit attacks such as those described above.
Among the known detection and monitoring systems of connected application, document U.S. Pat. No. 4,792,791 discloses a device for monitoring the quality of the lubricating oil of an engine through the corrosion of a resistant element which is part of an electric circuit.
When the resistant element is corroded by the oil in which it is immersed, its resistance varies, then this variation is recorded and considered as a sign of aging of the oil.
Exploitation of the resistance variation of a corrodible sensitive element is also disclosed in documents U.S. Pat. No. 4,675,662, U.S. Pat. No. 4,782,332 or in patent application FR-2,689,240 filed by the applicant.
Although such systems give satisfaction since they allow the aging of an oil or of another engine operating liquid to be monitored, they react only when the degradation or the aging of the oil is in a rather advanced state.
This type of detectors is not sensitive enough to detect for example corrosion of a small zone of the circuit, which would cause no resistance variation. In fact, most of them signal an anomaly only from a certain degradation level.
Besides, if the circuit is made from differents materials, it is not certain that the detector is sensitive enough to all the materials.